A loosely coupled transformer with mixed winding and electromagnetic shielding for contactless power transmission

The loosely coupled transformer is the key component of a contactless power transmission (CPT) system. In order to reduce the size of the loosely coupled transformer, mixed winding arrangement containing planar winding and vertical winding is proposed in this paper. However, because of the using of the vertical winding, the proposed transformer has a large part of leakage flux at the back of the core, resulting in low coupling coefficient k of the transformer. An aluminium sheet is attached to the back of the core as electromagnetic shielding to avoid this problem and improve the coupling coefficient. After that, the length of the aluminium sheet is optimised. A loosely coupled transformer with mixed winding and shielding is fabricated in the lab. The optimization of the length of the shielding is verified with experimental measurement to be very accurate. A contactless transformer with k of 0.583 and length of 73 mm is achieved. Compared with the previous transformer having k of 0.523 and length of 90 mm, the proposed transformer offers smaller size and higher k.